Lamarck's Genera of Shells. 225 



Xhe Patellae are widest at the posterior side, and the periphery 

 «f the shell is usually oval. They seem to live habitually in 

 the same place, though they probably have the power of 

 changing their situation from time to time. 



Linnaeus or Gmelin classed the fissurella, emarginula, navi- 

 eella, umbrella, pileopsis, calyptra;a, and crepidula, all under 

 the genus Patella. 



Most of the PatelljE have ribs, radiating from the summit to 

 the margin. 



Type. Patella cjranatina*. (Idem, Xm?2.) 



Shell angular, with numerous ribs and strice ; apex, both 

 within and without, purplish black. Antilles. 45 species. 

 PI. VII. Fig. 112. 



3d Family. 



Semi-Piiyllidiana. (2 genera.) 



Branchiae situated under the border of the mantle, and dis- 

 Jjosed in a longitudinal seiries, on the right side only of the 

 body. The animals breathe water. 



In the disposition of the branchiae, the mollusca of this family 

 liave considerable resemblance to those of the preceding, ex- 

 cept that in the Phyllidiana they occupy the whole of the 

 canal, which encircles the body between the border of the 

 mantle and the foot, whilst in the Semi-Phyllidiana they are 

 found only in that half of the canal which lies on the right 

 side, — whence the name. In other respects, the two families 

 differ considerably ; but, since the branchite are not placed, as 

 m the succeeding families, in an insulated cavity, Lamarck has 

 thought it necessary to assign them a distinct rank, in the order 

 of the Gasteropoda. 



1. Pleurobranchusf. 



Body crav.'ling, fleshy, oval-elliptic, covered by a projecting 

 mantle ; foot large and projecting like the mantle, so that the 

 two form an intermediate canal, and the body appears as if en- 



• Garnet-coloured. 



t From wxsyja the side , and ^5<«>X"'> Ijrunclna, the Htng'smlh kfiich fishes 

 breathe, 



Q 2 



